Vitamin D is a pleiotropic dietary hormone that protects against carcinogenesis. Epidemiologic and pre-clinical studies show that vitamin D is involved in prostate cancer prevention and may have a role in prostate cancer treatment. There is mounting evidence that inflammation is a risk factor for prostate cancer. Our overall hypothesis is that vitamin D3 is an anti-inflammatory agent in the prostate and this activity contributes to prostate cancer prevention by vitamin D3. The concept that anti-inflammatory agents may prevent prostate cancer is not new. However, long term prevention clinical studies with COX-2- selective inhibitors are not practical due to severe side effects and studies with non-prescription NSAIDS are difficult to run over long periods of time. Therefore, it is appealing to reduce prostatic inflammation, and likely systemic inflammation, by maintaining adequate vitamin D status. This new proposal is based on our previous published studies on the anti-inflammatory actions of vitamin D in prostate epithelial cells and preliminary results of the PI's funded K22 grant Significance of Vitamin D-Regulated MicroRNAs in Prostate Cancer Prevention. MicroRNAs are also crucial to inflammatory signaling and feedback loops. Global and specific changes in miR expression have been demonstrated in prostate cancer. We identified several inflammatory miRs that were regulated by vitamin D3 in prostate epithelial cells and clinical trial tissue. Men in this trial (N=60, completed at the University of Toronto) wre given 400IU, 10,000IU or 40,000IU of vitamin D3 (cholecalciferol) for 4-6 weeks prior to radical prostatectomy. Our preliminary work focused on prostatic epithelium, however, prostatic epithelial glands are surrounded by prostate stroma. It is well established the prostate stroma is involved in prostate cancer as the stroma has regulatory control over epithelial proliferation, differentiation and is a necessary mediator of the prostatic inflammatory response. In response to inflammatory stimulus, epithelial and stromal cells rapidly release cytokines that propagate the inflammatory response and recruit immune cells to the area. To interrogate the interplay between cell types, we have developed a three-dimensional co-culture in vitro model of inflammation using primary prostatic stromal and epithelial cells. Using this model, our preliminary data show that not only do prostate stromal cells produce different cytokines and microRNAs than epithelial cells, but that vitamin D3 abrogates different specific cytokines and microRNAs in each cell type. The experiments in this proposal will examine the hypothesis that the interplay between prostate stroma and epithelium is altered by vitamin D3; creating a micro-environment of decreased proliferation, increased differentiation and decreased inflammation. We propose a bedside-to-bench approach to first quantify the key genes and microRNAs in stromal tissue then assess these inflammatory mediators in a relevant in vitro model.